1. Field of the Invention
The present invention relates to a liquid crystal display apparatus such as a TV set or a display. In particular, the present invention relates to a liquid crystal display apparatus including a vertically aligned liquid crystal.
2. Description of the Related Art
A liquid crystal display apparatus includes a liquid crystal inserted between a pair of substrates. The pair of substrates include electrodes and alignment layers, respectively. The TN liquid crystal display apparatus that finds wide applications includes horizontal alignment layers and a crystal having a positive anisotropy of its dielectric constant when no voltage is applied, the liquid crystal is aligned substantially parallel to the horizontal alignment layers. When a voltage is applied thereto, on the other hand, the liquid crystal becomes substantially perpendicular to the horizontal alignment layers.
The TN liquid crystal display apparatus has the advantage that it can be made thin but has the disadvantage that the visual field angle is small. A method of improving this disadvantage and assuring a wide visual field angle is alignment division. In alignment division, each pixel is divided into two regions, so that the liquid crystal rises toward one side in one region and rises toward the opposite side in the other region. In this way, a wider visual field angle is assured by averaging the behavior of the liquid crystal in one pixel.
To control alignment of the liquid crystal, the alignment layers are normally rubbed. For alignment division, one region of the pixel is rubbed in a first direction using a mask, and the other region of the one pixel is rubbed in a second direction opposite to the first direction using a complementary mask. As an alternative, the whole alignment layer is rubbed in the first direction, and the one region or the other region of one pixel is selectively irradiated with ultraviolet rays using a mask thereby to create a pretilt difference between the one region and the other region.
In a liquid crystal display apparatus using horizontal alignment layers, it is necessary to carry out cleaning to clean the substrates formed having the alignment layers after rubbing. As a result, the fabrication of the liquid crystal panel is comparatively troublesome and the substrates may be polluted during the rubbing.
In a liquid crystal display apparatus using vertical alignment layers, on the other hand, the liquid crystal is aligned substantially perpendicular to the vertical alignment layers when no voltage is applied thereto and the liquid crystal is substantially parallel to the vertical alignment layers when a voltage is applied thereto. Also with a liquid crystal apparatus using the vertical alignment layers, the alignment layers are normally rubbed for controlling the alignment of the liquid crystal.
Japanese Unexamined Patent Application No. 10-185836 filed by the assignee of this application proposes a liquid crystal display apparatus capable of controlling alignment of the liquid crystal, without rubbing. This liquid crystal display apparatus is an aligned crystal display apparatus of a vertical alignment type, includes a liquid crystal having vertical alignment layers and a negative anisotropy of dielectric constant, and has alignment control structures (linearly arranged structures having projections or slits) on each of the pair of substrates for controlling the alignment of the liquid crystal.
This liquid crystal display apparatus of a vertical alignment type has the advantages that no rubbing is required and that the alignment division can be attained by the arrangement of the linearly arranged structures. With this liquid crystal display apparatus of a vertical alignment type, therefore, it is possible to secure a wide visual field angle and a high contrast. Elimination of the requirement of rubbing allows the cleaning after rubbing to be eliminated. Thus, the fabrication of a liquid crystal display apparatus is facilitated, and without any pollution on the substrates, which otherwise might occur at the time of rubbing, the reliability of the liquid crystal display apparatus is improved.
In the liquid crystal display apparatus of a vertical alignment type having alignment control structures (projections or a slits) on substrates for controlling alignment of the liquid crystal, it has been found that there are regions where the alignment of liquid crystal molecules is unstable, and there are problems regarding brightness and response speed, which must be improved.